Why do we make eye fixations to specific places? The standard account of the locus of fixations has been that constellations of co-located features serve as the targets of gaze [1]. Although it has been suggested that fixation locations may be determined by a surprise measure that calculates whether the distribution of features at a location is unexpected [2], this account is still feature-based.

Our own hypothesis is that task-based reward governs the choice of locations [3]. Numerous studies have established that reward can be seen as the basis of eye fixations via correlations at the neural level, but we have described a completely novel hypothesis: Fixations can reduce uncertainty in the state of a cognitive behavior's control program. We have predicted that, given that the central evaluation is reward-based, eye fixations should be made to the location that promises the most reward for uncertainty reduction. This hypothesis had been tested in a virtual reality simulation with humanoid models and shown to be superior to standard methods.

We now report that our hypothesis has been tested using human subjects' walking data [4]. When subjects walk by approaching pedestrians, they fixate them with a probability that varies predictably depending on ancillary tasks that the subjects are engaged in, such as following a leader. Our reward based model predicts that these variations in probability will have a mean of 0.17 with a standard deviation of 0.03 which is very close to the observed mean of 0.19. The closeness of this fit suggests that the feature-based account of eye fixations may need extensive revision.